Safety control for fuel burners



June 26, 1945. c s o 2,379,113

SAFETY CONTROL FOR FUEL BURNERS Filed Feb. 9, 1942 COMB/NED VALVE A/VD SWITCH Patented June 26, 1945 SAFETY CONTROL FOR FUEL BURNERS Charles K. Strobe], Pittsburgh, Pa., Robertshaw Thermostat Company,

assignor to Youngwood,

Pa., a corporation of Pennsylvania Application February 9, 1042, Serial No. 430,001

14 Claims.

This invention relates to safety controls for fuel burners and, more particularly, to electrically operated controls therefor.

Electrically operated fuel control apparatus has been arranged to permit supply of gaseous fuel to a main burner if a flame sensitive portion of the apparatus has previously been heated by a pilot burner. The flame sensitive device may take the form of an electrical resistance element having the characteristic of changing its resistance when heated and thus changing the value of the energizing current supplied to the fuel controlling member of the safety apparatus. Such apparatus is, however, unduly sensitive to small fluctuations in electrical resistance in various parts of the circuit, rendering the adjustment thereof more critical than is generally desirable.

An object of this invention is to maintain the safety features of such apparatus while eliminating the objectionable characteristics thereof.

Another object of the invention is to ensure positive operation of the fuel controlling member while leaving it fully responsive to the condition of the flame sensitive device.

Another object of the invention is to permit immediate recycling of the apparatus and return to normal operating conditions regardless of the manner in which the main operated.

Another object of the invention is to avoid reliance on the provision of a pilot burner and permit operation of the safety control directly on the main burner if desired.

Another object of the invention is to maintain desirable operating conditions for the ignition and fuel controlling devices to ensure dependable operation of these parts.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing, wherein is shown a schematic view of a safety control apparatus for a gaseous fuel burner embodying this invention.

Referring more particularly to the drawing, a gaseous fuel burner I is shown as being supplied with fuel by a main fuel pipe l2. The fuel supply is controlled by a main valve I4 which may qcontrol device is be either manually or thermostatically operated.

Interposed in the fuel supply pipe i2 between the main valve I 4 and burner ill is an electromagnetic or solenoid gas valve l6 of any known type which may be arranged, as in this instance, to be opened by energization of the solenoid and closed by gravity when deenergized.

For the purposes of this embodiment of the invention the safety control and ignition system is illustrated and described as operating directly upon the main burner l0. It will be understood, however, that while the apparatus lends itself .to such arrangement it is equally applicable to systems employing a pilot burner also. In such cases the pilot burner could receive its supply of fuel from the fuel pipe 12 either ahead of the solenoid valve IE or from between this valve and the main burner 10. Such choice of pilot connection depends upon whether complete shut-off of fuel is desired in case of electric power failure as will be apparent.

Electric current forthe operation of the apparatus is supplied by the line wires I8 connected to the primary of a transformer 20. The secondary of the transformer 20 is connected by a wire 22 to one terminal of a main switch which, in this instance, is incorporated in the main valve I4. Any suitable means may be used to close the switch when the main valve I4 is actuated to open position. The other terminal of the main switch of valve I4 is connected by a wire 24 to one end of a. series resistance 26, the other end of which is connected by a wire 28 with one end of a parallel mesh included in the circuit. The other end of the parallel mesh is connected by a wire 32 with one terminal of an ignition coil 34, the other terminal of which connects by means of a wire 36 with the other terminal of the secondary of the transformer 20.

The parallel mesh previously referred to includes several parts now to be described. One branch comprises an adjusting resistance 38 connected at one end by a wire 40 to the wire 32 and at the other end by a wire 42 to one end of a flame sensitive element or heat responsive device 44, the other end of which is connected by a wire 46 to the wire 28. The flame sensitive element 44 may be in the form of a coil of wire formed from material having normally a relatively low resistance and a positive temperature coemcient of resistance. Such elements are known as ballast resistors and will thus be referred to hereinafter, but other types of flame sensitive or heat responsive devices or thermal resistance elements having the required characteristics may be substituted.

The other branch of the parallel mesh comprises a constant resistance element 48 connected at one end by means of a wire 50 to the wire 28 and at the other end by a wire 52 to one terminal of the actuating coil of the solenoid valve 55 IS. A cut-out, preferably of the slow-acting bimetallic snap switch type, designated by the numeral 6| may be interposed in the wire 62 for protecting the solenoid valve coil in the event that an open circuit occurs in the ballast resistor 44. The other terminal of the solenoid valve coil is connected by a wire 56 to the wire 62, thus completing the circuit of the parallel mesh. As shown schematically the ignition coil 64 and the ballast resistor 44 are both housed within the chamber III which contains the burner l6 and are exposed to the flame thereof.

As desirable in apparatus of the kind described, means are provided to permit the ignition coil 34 to reach igniting temperature before the solenoid valve l6 opens and permits fuel to flow to the main burner It. In this instance, an initially closed switch 54 is utilized to shunt the solenoid valve l6 and prevent opening thereof for a specifled period of time.

Means are also provided for shunting the constant resistance element 48 for a specified period of time after closing of the main switch l4.

' The shunt may be established in the same manner as that for the solenoid valve I6 but should be effective for a longer period of time. Accordingly, a second initially closed switch 56 is provided for the purpose and both switches may form part of a control relay conveniently operated by a single coil 58 having one end connected by a wire 66 to the wire 36 and the other end thereof connected by a wire 62 to the wire 24.

The parallel circuit connection for the switches 54 and 56 may be made by connecting one terminal of the switch 54 to the wire 55 by means of a wire 64 and connecting oneeterminal of the switch 56 to the wire 50 by means of a, wire 66. The remaining two terminals of the switches 54 and 56 may be connected by a common wire 68 to the wire 52 between the cut-out 5| and solenoid valve It, thus completing the parallel circuit and causing both the solenoid valve 16 and the constant resistance element 48 to be shunted when the switches 54 and 56 are closed.

The switches 54 and 56 are preferably of the mercury tube type disclosed in Patents Nos. 1,778,439 and 2,224,873 among others, to which reference may be had for a fuller description. In the present embodiment the switch 54 may have a time-delay of five seconds before opening and an instantaneous closing upon operation of the main switch l4.

For a purpose which will appear hereinafter, the switch 56 which has been described as having a longer time delay before opening than switch 54 is adapted to maintain the constant resistance element 48 shunted for a longer period of time than the switch 54 maintains the solenoid valve [6 shunted. The switch 56 need not have an instantaneous closing action upon opening of the main switch of valve 14, as is desirable in the case of the switch 54, it being only necessary that it assume a closed position before opening of the switch 54. Accordingly, in this embodiment the switch 56 may be arranged to open after a period of thirteen seconds has elapsed from the time of opening of the switch 54. In view of the short time delay in opening of switch 54, preferably flve seconds as stated, the switch 56 must almost necessarily have an instantaneous closing action also.

The operation of the device is as follows. Manual or thermostatic closing of the main switch of valve l4 effects opening of this valve, as described, and permits fuel to flow in the main fuel pipe 12 as far as the solenoid valve IS. The

current from the transformer 26 is conducted by the wires 22 and 24 through the main switch of valve l4 to the series resistance 26. The wire 26 conducts the current from the series resistance 26 to the jimction of the parallel mesh. As both the switches 54 and 56 are initially closed, the current will flow by way of the wire 56 to the switch 56 and by the common wire 66 to switch 54 from where it is conveyed by way of wire 64 to the other junction of the parallel mesh. The wire 32 conducts the current from this end of the parallel mesh to the ignition coil 34 which becomes energized by completion of the circuit to the transformer 20 by the wire 36.

The switch 54 which has the shorter timedelay period will open after the specified five seconds, which is suificiently long for the ignition coil 34 to reach igniting temperature. Opening of the switch 54 removes the shunt from the solenoid valve l6 and the current then passes from the switch 56 by way of the common wire 68 and the wire 52 to one terminal of the actuating coil of the solenoid valve i6. As the other terminal of the solenoid valve I6 is connected by the wire 55 to one end of the parallel mesh and the circuit through the ignition coil 34 is completed as previously described, the solenoid valve [6 thereupon is actuated to open position. The fuel in the main fuel pipe l2 then flows to the main burner I0 where it is ignited by the ignition coil 34 to produce a fiame at the main burner.

The opening of the switch 54 as described also introduces the other branch of the parallel mesh, comprising the ballast resistor 44 and the adjusting resistance 36, into the circuit. The combined effect of the ballast resistor 44 and adjusting resistance 38 is, however, insuflicient to prevent opening of the solenoid valve l6, it being apparent that the ballast resistor 44 is then unheated by the burner flame and its resistance has accordingly not increased except insofar as the current flowing thereto causes heating thereof. It will be apparent that the selection of asuitable established value of resistance for the ballast resistor depends upon the voltage to be used in the system and may vary in accordance therewith and with the results sought to be obtained. Under the circuit conditions so established the current to the solenoid valve coil is arranged to be sufficient for positively opening the solenoid valve l6 simultaneously with the opening of the switch 54.

After the second time-delay period of thirteen seconds has expired, the switch 56 opens and introduces the constant resistance element 46 in series circuit with th solenoid valve l6. The combined effect of the ballast resistor 44, when unheated by the burner fiame, and the constant resistance element 46 together with the other parts of the circuit thereof, is suficient to reduce the value of the current through the solenoid valve l5 and cause it to close. However, after the specified thirteen seconds delay, the ballast resistor 44 has had time to become heated by the fiame and increase the resistance of the shunt circuit around the solenoid valve to such a value that suiflcient current flows through the valve coil to cause the valve to remain open. This shunt circuit may be traced by way of the wire 46 which connects with wire 28 at one end and with the ballast resistor 44 at the other, then by way of wire 42 to the adjusting resistor 36 and through wire 40 back to wire 32.

It will be apparent, moreover, that if at any 2,379,113 time during operation of the apparatus the flame of the main burner Illceases, then the ballast resistor 44 will cool and its resistance be lowered sufliciently to render the current through the solenoid valve coil insuflicient to retain the solenoid valve IS in open position whereupon this valve will close to shut off the fuel supply to the burner.

Should the ballast resistor 44 become opencircuited, as from fracture or other destructive influence, during the period of normal running of the apparatus, then the cut-out will prevent the solenoid valve from remaining open without this protection. The excess current which will be diverted to the circuit of the solenoid valve upon failure of the ballast resistor will cause the cut-out to operate and open the circuit. During the starting period when the current to the solenoid valve is large the cut-out is shunted by the switch 56 which serves to reduce the current thereto substantially below operating value. The shunt established by the switch 56 is removed when the specified timedelay expires and the protection of the cut-out is present during the running period.

Operation of the switch of the main valve l4 in an on-off-on cycle will cause the foregoing sequence of events to be repeated due to the reset features of the switches 54 and 56. Thus, a period for purging the vicinity of the main burner In of unburned fuel is provided for a period at least as long as the switch 54 takes to open. Where inclusion of a pilot burner is desired then the ignition coil 34 and ballast resistor 44 would be located near the pilot burner flame instead of the main burner flame. Only these elements need be located in the chamber of the oven or like device so that no exposure of any other elements of the apparatus to the heat or fumes emanating from the burner is required.

Since the temperature condition of the ballast resistor 44 does not influence the actuation of the solenoid valve 16, but only the holding and release of the valve, the circuit need only be adjusted to obtain the proper release current in the valve actuating coil under operating conditions. Thus, the circuit adjustments areless critical than in apparatus where the temperature condition of the ballast resistor is relied upon to actuate and release the valve, No chattering of the solenoid valve occurs due to its positive actuation as soon as the first time delay switch opens.

The circuit arrangement described and shown herein permits considerable variation in the value of the respective resistances without detracting from the desired operating characteristics. Moreover, while the preferred form and arrangement of parts has been illustrated and described, it will be apparent that the apparatus is not limited to this particular embodiment, but various changes may be made within the scope of the following claims.

I claim:

1. In combination, a burner, an electromagnetic valve adapted upon being moved to open position to establish a condition desirable only when the burner is ignited, an electrical resistance element in shunt with said valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, and means for introducing additional electrical resistance automatically in series circuit with said valve after said elements has had time to become heated, said additional resistance being sufflcient to cause closure of said valve unless said element has become heated.

2. A safety control for fuel burners comprising in combination, an electromagnetic valve movable between open and closed positions to control the supply of fuel to the burner, means subject to the heat of said burner and electrically connected to said valve for varying the supply of current thereto, said current variation being insuflicient to cause movement-of said valve, a resistance element electrically connected to said means and valve and effective to cause movement of said valve unless said means is heated, and an automatic control device for introducing said element after said means has had time to become heated.

3. A safety control for fuel burners comprising in combination, an electromagnetic valve movable between open and closed positions to control the supply of fuel to the burner, a thermal resistance element in shunt with said valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, a constant resistance element connected in series circuit with said valve and operable to cause movement thereof to closed position unless said thermal element is heated, and a time delay switch operable for introducing said constant resistance after said thermal element has had timeto become heated.

4. A safety control apparatus for fuel burners comprising in combination, a normally closed solenoid valve intercepting the supply of fuel to the burner, an energizing circuit for said solenoid valve, a thermal resistance element in shunt with said valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, a constant resistance element in said energizing circuit and operable to cause movement of said valve from open to closed position unless said thermal resistance is heated, and a control relay having a timing element in shunt with said constant resistance element and operable to delay energization thereof until said thermal element has had time to become'heated.

5. A safety control apparatus for fuel burners comprising in combination, a normally closed solenoid valve intercepting the supply of fuel to the burner, an energizing circuit for said solenoid valve, a thermal resistance element in shunt with said valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, a constant resistance element in said energizing circuit and operable to cause movement of said valve from open to closed position unless said thermal resistance is heated, and a control relay having a mercury tube switch in shunt with said constant resistance element and being normal closed, said switch being automatically actuated to open position but with time delayed operation upon energization of said energizing circuit, said time delay being sufficient to permit said thermal element to become heated before said constant resistance element is energized.

6. A safety control apparatus for fuel burners comprising in combination, a normally closed solenoid valve intercepting the supply of fuel to the burner, an energizing circuit for said solenoid valve, a thermal resistance element in shunt with said valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, a constant resistance element in said energizing circuit and operable to cause movement of said valve from open to closed position unless said thermal resistance is heated, and a control relay having a mercury tube switch in shunt with said constant resistance element and being normally closed but actuable to open position with time delayed operation upon energization of said energizing circuit, said time delay occurring only on opening movement to permit heating of said thermal element before energization of said constant resistance with substantially immediate resetting to closed position upon deenergization of said circuit.

7. A safety control apparatus for fuel burners having means for controlling the supply of fuel thereto, said apparatus comprising an electric igniter for said burner energized by operation of said controlling means, a normally closed solenoid valve in series circuit with said igniter and intercepting the fuel supply to said burner, a control relay device having a timing element connected in parallel circuit with said solenoid valve and operable to delay actuation thereof to open position until the igniter has reached igniting temperature, a thermal resistance element connected in another parallel circuit with said solenoid valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, a constant resistance element connected in series circuit with said solenoid valve and operable to cause movement of said valve from open to closed position unless said thermal resistance is heated, and a second timing element associated with said relay device and connected in parallel circuit with said constant resistance element and operable to delay energization thereof until said thermal element has had time to become heated.

8. A safety control apparatus for fuel burners having means for controlling the supply of fuel thereto, said apparatus comprising an electric igniter for said burner energized by operation of said controlling means, a normally closed solenoid valve in series circuit with said igniter and intercepting the fuel supply to said burner, a control relay device having a normally closed switch connected in parallel circuit with said solenoid valve, said switch being automatically actuated to open position but with time delayed action upon operation of said controlling means and being substantially immediately reset to closed position upon further operation of said controlling means, said time delay being sufflcient to permit said igniter to reach igniting temperature, a thermal resistance element connected in another parallel circuit with said solenoid valve and exposed to the burner flame, said element being adapted to increase its resistance when heated, a constant resistance element connected in series circuit with said solenoid valve and operable to cause movement of said valve from open to closed position unless said thermal resistance is heated, and a second normally closed switch associated with said relay device and connected in parallel circuit with said constant resistance element, said switch being automatically actuated to open position but with longer time delayed action than the first said switch upon operation of said controlling means and being reset to closed position upon further operation of said controlling means in less time than the said time delayed action of the first said switch, said longer time delayed action permitting said thermal element to become heated before energization of said constant resistance element.

9. In a safety control system for fuel burners asvar is having a starting and a running period, electrically operable means having an open position for supplying fuel to the burner, an energizing circuit for said fuel supplying means including resistance element so proportioned and arranged that during the starting period sumcient current is supplied to said fuel supplying means for actuation thereof to open position but during the running period only sufficient current to maintain said position, means operable for opening said circuit upon an increase in current to said fuel supplying means beyond that required during the running period, and a switch operable for introducing said circuit opening means after said starting period.

10. In a safety control system for fuel burners having a starting and a running period, electrically operable means having an open position for supplying fuel to the burner, an energizing circuit for said fuel supplying means including resistance elements so proportioned and arranged that during the starting period sufficient current is supplied to said fuel supplying means for actuation thereof to open position but during the rurming period only suflicient current to maintain said position, means operable for opening said circuit upon an increase in current to said fuel supplying means beyond that required during th running period, and a control relay having a timing element connected in parallel circuit with said circuit opening means for conducting the current through a path of substantially less resistance than said means during the starting period, said parallel circuit being open during the running period by operation of said timing element.

11. In a safety control system for fuel burners. electrically operable means for controlling the supply of fuel to the burner, said means being operable to cause supply of fuel to the burner when sufiicient current is supplied to said means, means subject to the heat of the burner and adapted for varying the supply of current to said controlling means in accordance with the thermal condition of said heat subject means due to the presence or absence of heat at the burner, means cooperable with said heat subject means for rendering said current supply insufllcient for the purpose aforesaid in one said condition of said heat subject means in the absence of heat at the burner, means for rendering said controlling means inoperable to cause said fuel supply upon occurrence of a condition of current supply increase beyond that required for the purpose aforesaid, and means for rendering the last two said means effective under said conditions after said heat subject means has had time to become heated.

12. In a safety control system for fuel burners having a source of electrical energy, comprising in combination, electrically operable means connected to said source for controlling the supply of fuel to the burner, said controlling means being actuable to a fuel supplying position when energy of sufficient value is supplied thereto and being movable to a position for preventing said fuel supply when energy of insufllcient value is supplied thereto, a thermal resistance element located to be heated by the burner and electrically connected to said controlling means for varying the energy value supplied thereto, said energy variation being insuflicient to cause movement of said controlling means from the fuel supplying position, a second resistance element electrically connected to said controlling means and thermal resistance element, said second resistance element being effective upon energization thereof to cause the last said movement unless said thermal resistance element is heated, and a control relay having a timing element electrically connected to said second resistance element for delaying said energization thereof until said thermal resistance element has had time to become heated.

13. A safety control system for fuel burners having a source of electrical energy, comprising in combination, electrically operable means connected to said source for controlling the supply of fuel to the burner, said controlling means being actuable to a fuel supplying position when energy of suflicient value is supplied thereto and being movable to a position for preventing said fuel supply when energy of insuflicient value is supplied thereto, an electric igniter for the burner and connected to receive energy from the source, a control relay having a timing element electrically connected with said controlling means for delaying said actuation thereof for a predetermined perlod following energization of said igniter, a thermal resistance element located to be heated by the burner and electrically connected to said controlling means for varying the energy value supplied thereto, said energy variation being insuflicient to cause movement of said controlling means from the fuel supplying P sition, a second resistance element electrically connected to said controlling means and thermal resistance element, said second resistance element being effective upon energization thereof to cause the last said movement unless said thermal resistance element is heated, and a second timing element associated with said relay and electrically connected to said second resistance element for delaying said energization thereof for a predetermined period during which said thermal resistance element has time to become heated.

14. A safety control system for fuel burners having a source of electrical'energy, comprising in combination, electrically operable means connected to said source for controlling the supply of fuel to the burner, said controlling means bein actuable to a fuel supplying position when energy of sufficient value is supplied thereto and being movable to a position for preventing said fuel supply when energy of insufficient value is supplied thereto, an electric igniter for the burner, a thermal resistance element located to be heated by the burner for varying in resistance value and connected in shunt with said controlling means, said variationbeing insufficlent to reduce the energy value to said controlling means sumeiently to cause movement thereof from the fuel supplying position, an energizing circuit including the source, said igniter, said controlling means and a second resistance element efl'ective upon energization thereof to cause the last said movement unless said thermal resistance element is heated, a control relay having a timing element connected in shunt with said controlling means for delaying said actuation thereof for a predetermined period following energization of said igniter, and a second timing element associated with said relay and connected in shunt with said second resistance element for delaying said energization thereof for a predetermined period during which said thermal resistance element has time to become heated.

CHARLES K. STROBEL 

